1. Field of the Invention
The present invention relates to a roller bearing in which a crowning is formed on at least one of an inner ring raceway, an outer ring raceway, and a roller rolling contact surface, and a method of designing the crowning.
2. Description of Related Art
In a roller bearing, a crowning is conventionally formed on an outer ring raceway, an inner ring raceway, and a roller rolling contact surface. An edge load applied to end sections of the contacting sections between the raceways and the rolling contact surface is prevented, thereby extending the fatigue life of the roller bearing.
A curved line expressed by a logarithmic function is used for a profile of the crowning formed in the roller bearing. A function proposed by Lundberg is widely known as the crowning curve expressed by a logarithmic function (refer to Non-patent Document 1: Lundberg, G, Elastic Contact Between Two Semi-Infinite Bodies, Forschung auf den Gebiete des Ingenieurwesen, 5[1939], pp. 201-211). A function proposed by Johns-Gohar (refer to Non-patent Document 2: Johns, P. M. and Gohar, R., Roller bearing under radial and eccentric loads, Tribology International, 14[1981], pp. 131-136) is known as a practical modification of the crowning curve.
However, in the crowning curve based on the Johns-Gohar function, contact pressure is slightly high between the raceways and the rolling contact surface at end sections of a crowning forming section. The edge load cannot be sufficiently prevented.
Therefore, the inventors of the present invention have proposed a crowning curve in which new design parameters are introduced to the Johns-Gohar function to achieve uniformity in the contact pressure placed between the raceways and the rolling contact surface (refer to Patent Document 1: Japanese Patent Laid-Open Publication No. 2006-52790). In the design of a roller bearing to which the crowning curve is applied, a fraction size and an initial value search range of the above-mentioned design parameters are determined. Then, an objective function is determined for a combination of design parameters obtained by the initial value search range and the fraction size. A combination of design parameters of which the objective function is optimal is used as initial values. The initial values are further strictly optimized by a mathematical optimization technique, and the crowning curve is determined. The crowning formed in the roller bearing is thus designed. Another crowning curve is proposed in Patent Document 2.    Non-patent Document 1: Lundberg, G, Elastic Contact Between Two Semi-Infinite Bodies, Forschung auf den Gebiete des Ingenieurwesen, 5 (1939), pp. 201-211    Non-patent Document 2: Johns, P. M. and Gohar, R., Roller bearing under radial and eccentric loads, Tribology International, 14 (1981), pp. 131-136    Patent Document 1: Japanese Patent Laid-Open Publication No. 2006-52790    Patent Document 2: Japanese Patent Publication No. 3731401